The present invention relates to a dissimilar metal joining method that utilizes eutectic bonding.
In the case of joining two dissimilar metal materials together in the same way as in the case of joining similar metal materials, intermetallic compounds are often formed at a joint between the dissimilar metal materials. For example, hard, brittle intermetallic compounds such as Fe2Al5 and FeAl3 are formed when a steel material and an aluminum alloy material are welded to each other. It is thus desirable to limit the formation of the intermetallic compounds during the welding in order to secure a sufficient joint strength between the metal materials. Herein, the aluminum alloy material has a closely packed, solid oxide film at a surface thereof. Although the oxide film can be removed through the application of a large amount of heat, the intermetallic compounds grow in thickness by such high heat application and cause a weakening of the joint between the metal materials.
For these reasons, it is common practice to join dissimilar metals by mechanical fastening means such as bolts or rivets even though the mechanical fastening means however raises a problem of increases in weight and cost. It is conceivable to join dissimilar metals by friction pressure welding. However, the applicability of the friction pressure welding is limited to the joining of symmetrical rotary members. It is further conceivable to join dissimilar metals by explosion welding or hot rolling, but the explosion welding and the hot rolling are not preferred in view of the process equipment and efficiency.
In order to solve the above problems, various improvements have been made to dissimilar metal welding processes. Japanese Laid-Open Patent Publication No. 4-127973 (hereinafter abbreviated as “JP 4-127973”) proposes a process in which dissimilar metals are joined together by preparing a clad metal material consisting of two metals of the same kinds as the respective dissimilar metals, interposing the clad metal material between the dissimilar metals in such a manner that the metals of the same kind come into contact, and then, resistance welding these metals to each other. Japanese Laid-Open Patent Publication No. 6-039558 (abbreviated as JP 6-039558) proposes a process in which a steel material and an aluminum alloy material are joined together by plating a surface of the steel material facing the aluminum alloy material with an aluminum alloy containing 20 wt % or greater or pure aluminum and resistance welding the aluminum plating layer to the aluminum material with little melting of the steel material. Japanese Laid-Open Patent Publication No. 2001-252777 (hereinafter abbreviated as “JP 2001-252777”) and Preprints of National Meeting of Japan Welding Society (vol. 61, pp. 380, 1997) propose processes in which dissimilar metals are welded together by irradiating a YAG laser from one metal side in such a manner as to control base metal diffusion and weld metal composition and to limit the formation of intermetallic compounds between the dissimilar metals.